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IBC vs UBC vertical acceleration

[Subject Prev][Subject Next][Thread Prev][Thread Next] Preface: In the 2001 CBC, they amended load combinations in 1612.2 (eqs 12-5 and 12-6) in such a way that you could not be forced to subtract 0.5CaID from the already reduced 0.9D value for dead load effects. (Equation 12-6 was re-written to be 0.9D +/- 1.0*rho*Eh).

This makes sense, since the 0.5CaID value was created solely to make up for the "missing" 0.2 factor on Dead Load that appeared when the positive dead load factor was reduced to 1.2 (between the '94 and '97 codes). It makes no sense to use this factor to further reduce the 0.9 coefficient in equation 12-6.

Question: Now - I am trying to work with the IBC/ASCE 7 - and I do not see any provision for this. It appears that if you plug IBC equations 16-50 and 16-51 (or 16-28/16-29 for 2000 IBC) into the load combination equations 16-5 and 16-6, that you will end up reducing the Dead load effects by taking 0.9D minus another 0.2Sds*D.

So, for a case where Sds = 1.0, you would end up with a DL effect of 0.9 minus 0.2 = 0.70*D. Is this correct?

Thanks,

Glen

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